Direct and indirect responses to selection on individual body weight in the Pacific oyster (Crassostrea gigas)

Three experiments were performed to examine the heritability of body weight among adult Pacific oysters (Crassostrea gigas) evaluated in Yaquina Bay, Oregon, USA, and to determine if selection on individual body weight could result in changes in offspring survival and yield. The first two experiments utilized midparent-offspring regressions to estimate the heritability (h²) of adult oyster body weight and the coheritability (h_x,y) between adult midparent body weight and offspring performance, including juvenile average body weight, survival and yield as well as adult survival and yield. In Experiment 1 both parents and offspring were evaluated in an “upriver” environment in Yaquina Bay. In Experiment 2 parents were evaluated in a “downriver” environment, while offspring were evaluated in an “upriver” environment. Experiment 3 contrasted average body weight, survival, and yield of offspring (evaluated upriver) derived from three large sires and three small sires mated to the same five females that were chosen at random (all parents evaluated downriver). In Spring 2002, 12 full-sib families from Experiment 1, 19 families from Experiment 2, and 26 families from Experiment 3 were stocked into lantern nets and suspended in Yaquina Bay. Measurements of yield (kg tier^− 1), average body weight (g), and survival (%) were recorded after one and two growing seasons in the field. Heritability estimates for adult body weight at harvest ranged from 0.313 (± 0.083) in Experiment 1 to 0.003 (± 0.073) in Experiment 2. In Experiment 3, average body weight did not differ between offspring derived from large sires and offspring derived from small sires (P = 0.47). Significant negative coheritability estimates were observed between adult midparent body weight and offspring survival in both Experiment 1 and Experiment 2. Significant negative coheritability estimates between adult midparent body weight and offspring yield were observed in Experiment 2 but not in Experiment 1. In Experiment 3, offspring derived from large sires had significantly lower survival and yield than offspring derived from small sires. These results show adult oyster body weight to be heritable but also subject to site-specific adaptation such that selection in the downriver Yaquina Bay environment was ineffective at changing average body weight in the upriver environment. Negative coheritability estimates between performance traits indicate that adult oyster body weight may be a poor indirect measure of oyster yield potential, and that selection solely for increased body weight could lead to a decrease in offspring yield.     

Fat or lean? The quantitative genetic basis for selection strategies of muscle and body composition traits in breeding schemes of rainbow trout (Oncorhynchus mykiss)

Quantitative genetic analyses of fish composition have been strongly biased towards lipid deposition, rather than protein deposition. This is partly at odds with desires of the modern aquaculture industry, to improve the efficiency of lean growth. Using a quantitative genetic approach, we examined the selection potential in both protein and lipid components of wet weight growth in rainbow trout over a two-year growth period. Two diet treatments were applied to test the hypothesis that an experimental, high protein, low lipid diet (HP) would enhance selection potential compared to the current modern, normal protein, high lipid diet (NP). We found that lipid traits (lipid body weight, percent muscle and body lipid; h² = 0.40) were more heritable than corresponding protein traits (protein body weight, percent muscle and body protein; h² = 0.18), indicating a higher selection potential for lipid traits. The results revealed further that breeding for improved lipid composition over the whole growth period is easier than for protein composition. This was shown by the high favourable genetic correlations between differently aged fish for lipid traits. In contrast, the respective correlations for protein traits were low or even negative. Similarly, the genetic correlations between muscle and body composition were higher for lipid than for protein, enhancing selection efforts to change lipid traits. Heritabilities increased with age, implying that selection practiced on old (> 800 g) rather than young (< 60 g) fish should be more effective in achieving a compositional response. Although the diet had a significant effect on the composition traits, there was no general trend for diet differences in heritabilities of either protein or lipid traits. Thus, the hypothesis of increased selection potential on HP diet was not supported. In conclusion, lipid traits are both more variable and exhibit more favourable genetic architecture for selection compared to protein traits.     

Heritability estimates for processing and quality traits in common carp (Cyprinus carpio L.) using a molecular pedigree

Heritability estimates with a microsatellite parentage assignment based pedigree are of special interest in common carp cultured under traditional pond conditions. This method reduces common environment effects as all families can be grown immediately after hatching mixed in the same pond. We applied this method to study genetics of growth and processing traits in common carp at market size (1.5 kg and more). The experimental progeny was established by crossing 147 two-year old males and 8 females (six to eight-year old) of Hungarian synthetic mirror carp population. The fish grew up through three vegetation seasons and at the end a sample of 331 fish was examined for biometrical traits (standard length, body weight, relative head length, relative body height, relative body width), percent fat and processing traits (% processed body, % fillets with skin, % fillets without skin). It was shown that sex had a significant effect on most traits: females were larger and fatter than males, and they had both higher percent processed body and percent fillet with skin. Standard length, body weight, percent fat and relative head length had a high heritability (> 0.5), while relative body height, relative body width, percent processed body and fillet yields had a medium heritability (0.2–0.5). We found relatively high positive genetic correlations between body size (standard length and body weight) and percent fat (0.71 and 0.59, respectively), favourable genetic correlations between body size and percent processed body (0.69 for standard length and 0.74 for body weight) and between body size and fillet yields (0.50–0.77). Genetic correlations between body size and body shape (relative head length, relative body height and relative body width) were weak to moderate, thus selection for better growth should have little impact towards more rotund shape. Relative head length had strong negative correlation (− 0.7 to − 0.9) with percent fat, percent processed body and percent fillet yields. This means that indirect selection for reduced relative head length should be effective in improving of fillet yield.     

动态性状遗传参数的估计方法

本文在建立个体动态性状数学模型同时，计算了模型参数估计误差方差，依此标准化模型参数，完善了动态性状遗传参数的估计方法。     

脊尾白虾耐盐碱性状遗传力和遗传相关的估计

应用数量遗传学原理和全同胞组内相关法估计50日龄脊尾白虾(Exopalaemon carinicauda)耐盐碱性状的遗传力和遗传相关。采用定向交尾方式构建脊尾白虾50个全同胞家系(包括42个半同胞家系),利用SPSS软件的一般线性模型(GLM)对各家系盐碱胁迫的存活时间进行方差分析,估计脊尾白虾耐盐碱性状的遗传力和遗传相关。结果显示,脊尾白虾耐盐碱性状的遗传力为0.18~0.60,其估计值未达到显著水平,属于中等遗传力;50日龄脊尾白虾耐盐碱性状与体长的遗传相关和表型相关分别为-0.401和0.127,耐盐碱性状和体重的遗传相关和表型相关分别为-0.196和0.033,耐盐碱性状与体长、体重的相关程度较低。本研究表明,选择育种对于脊尾白虾耐盐碱性状的改良具有较大潜力,且以耐盐碱性状为选育指标,不会对脊尾白虾体长和体重产生显著影响。     

甘蓝几个性状的配合力和遗传分析

利用６个甘晚熟热本自交系，按双列杂交法配制３０个组合进行主要数量性状配合和和遗传分析。结果表明，甘蓝帮叶比、紧实度、中心柱长、病毒病、黑腐病５个性状在各亲本系间的配合力有差异，亲本系之间选择有差异，并在一代杂种中能配最佳组合；紧实度、病毒病、黑腐病３性状以广义遗传力为主，杂种优势利用是育种的重要途径；中心柱长、帮叶比二性状以狭义遗传力为主，着重一般配合力的选择，系统选择双亲，可获较好杂种。     

甘蓝型杂交油菜亲本含油量及主要农艺性状配合力与遗传力分析

研究甘蓝型优质杂交油菜亲本产量、含油量及主要农艺性状的配合力和遗传力,为杂交油莱育种选择优良亲本和组配强优势组合提供理论依据。选用新育成的6个性状优良的甘蓝型油菜隐性核不育系母本,9个甘蓝型油菜优质骨干亲本作父本,采用NCⅡ不完全双列杂交模式,分析54个杂交组合的含油量及8个主要农艺性状的配合力与遗传力。结果表明,在综合一般配合力上,6个不育系母本的优劣顺序为2310A2007A2225A2043A2081A2326A,9个父本品系的优劣顺序为301633773354329931153028、314630743320,产量特殊配合力最好的组合是2225A×3115,含油量特殊配合力最好的组合是2225A×3074,性状遗传力以千粒质量广义遗传力最高,其次为含油量和有效分枝高。2310A、2007A、2225A和3377、3354、3115是综合性状较好、一般配合力较高的不育系和恢复系,产量、含油量的一般配合力和特殊配合力均较高。     

鲜食糯玉米货架期苞叶相关性状的配合力及其遗传效应分析

为了明确鲜食糯玉米货架期间苞叶相关性状的配合力及其遗传效应，选用6个自交系为父本、6个自交系为母本，按不完全双列杂交设计组配得到36个组合，对6个苞叶性状进行配合力分析和遗传参数估计。结果表明，苞叶含水量、苞叶层数、苞叶长、苞叶宽和苞叶总面积的一般配合力方差分析均达极显著水平，苞叶叶绿素含量达显著水平。苞叶性状遗传参数基因型方差均大于环境方差，主要受基因型的影响；GCA方差均大于SCA方差，表明以基因的加性效应为主。各性状的狭义遗传力大小依次为苞叶层数>苞叶叶绿素含量>苞叶宽>苞叶长>苞叶含水量>苞叶叶面积，苞叶含水量、苞叶叶绿素含量、苞叶长、苞叶宽、苞叶层数的狭义遗传力均大于50%，表明这些性状可以在早代进行选择。